In the color diffusion transfer process, photographic materials for a color diffusion transfer process are popularly used for "instant photography", because color prints can be instantly obtained by utilizing dye images imagewise transferred by diffusion (refer to detailed explanations in, for example, Photographic Science and Engineering, Vol. 20, No. 4, pages 155-164, July/August 1976).
This kind of sensitive material must be processed in situ just after photographing. Since the photography is carried out without regard to the season, for example, in summer or winter, or the region, for example, in the tropical zone or the frigid zone, the processing temperature varies according to the season or the region. Accordingly, the prior sensitive materials are undesirable because their gradation varies according to the processing temperature causing deterioration of the quality of images. Particularly, the sensitive materials for a color diffusion transfer process which comprise a direct reversal photographic emulsion layer are undesirable due to the creation of a soft or hard tone at a low or high temperature as compared with those using a negative emulsion as described in Japanese Patent Application (OPI) 90534/74 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application," hereinafter the same). Controlling the gradation has been described in U.S. Pat. No. 4,035,185 and Research Disclosure, vol. 151, No. 15162, wherein two kinds of direct reversal photographic emulsions having each a different gradation are mixed or emulsions having different sensitivities are mixed. However, even if mixed emulsions are used, the gradation varies according to the processing temperature, and the resulting prints have an unstable image quality. It is therefore desired to develop sensitive materials capable of forming images having a desired gradation which do not vary according to the processing temperature.